<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script type="text/javascript">
			function eva(){
				var a=document.getElementById("jsnum").value;
			    document.getElementById("scjg").innerHTML=(eval(a));
				
			}
			
		</script>
	</head>
	<body>
		
		<input type="text"  id="jsnum" value="" />
		<input type="button"  id="jg" value="="  onclick="eva()"/>
		<p id="scjg"></p>
	</body>
</html>
